Database management systems (DBMS's ) are well known. A database comprises a collection of data objects. Each object is defined by one or more attributes, which describe the object. Two or more different objects within a database may have the same attributes. The attributes may have one or more values, which may be quite complex. The objects are typically indexed by their attributes. For example, given an attribute value, a list of objects that have the same attribute and the same attribute value may be created.
A common example is a database in which the objects are documents. Because documents are most often identified by searching for keywords (i.e., the words contained in the document), it is common to use the keywords as attributes for indexing the document. The position of a given keyword within a document is the value of the keyword attribute. If the keyword appears two or more times in the document, the keyword attribute has two or more values. If the same keyword appears in a second document (object), then the second document has an attribute for the same keyword, with a respective position (attribute value).
It is frequently necessary to search a database for a pair of words within proximity to one another. For example, if the user wishes to query the database about the Governor of Pennsylvania, the desired information might appear in a document as "Governor of Pennsylvania" or "Pennsylvania Governor". To find documents that include either phrase, the user queries the database for documents in which "Pennsylvania" and "Governor" appear in any order within two words of one another.
In prior art database querying methods known to the inventors, proximity searching has only been performed on up to two strings at a time.
Alternate database querying methods are desired, by which proximity searches may be extended to allow document search queries that include three or more keywords.